A. Field of Invention
This invention relates to hearing aid compatible devices providing inductive coupling of an audio signal to a hearing aid having a telecoil. More particularly, the invention relates to systems and methods for optimizing the strength and orientation of the inductive field of a hearing aid compatible device.
B. Background and Description of Related Art
Hearing aids typically use a small microphone and amplifier to pick up sound and amplify it for persons with hearing related disabilities. However, this arrangement can cause feedback when a telephone's earpiece is placed up to the wearer's ear. Additionally, the presence of background noise affects the speech comprehension of people with partial hearing much more adversely than that of people with normal hearing. People with partial hearing thus require a high signal-to-noise ratio to optimize their speech discrimination.
A hearing aid telecoil is a small, tightly wrapped piece of wire that, when activated, picks up the voice signal from an inductive field that is emitted from hearing aid compatible (HAC) devices, such as telephones. Such inductive fields may be generated by voice-coil type speakers, or transmitting telecoils contained in the device. Thus, telecoil-equipped hearing aids are able to bypass background noise, and prevent the phenomenon of feedback.
However, nearby electromagnetic interference (EMI) may also be picked up by the telecoil, creating interference with the desired voice signal. For example, power transformers, fluorescent lighting, trains and the operation of digital wireless telephones can cause EMI that can be picked up by telecoils.
For example, with respect to digital wireless phones, the EMI may be caused by several sources. One such source is the actual digital radio frequency (RF) transmission of the communication signal. This pulsing signal appears to induce continually varying current in the small wires of the hearing aid. Another source of EMI is extraneous radiation from the wireless phone's battery, components and wiring. For instance, in a time-sharing, multiplex network, such as a TDMA or GSM network, the RF transmitter of the phone turns on and off at the rate of multiplexing, which typically falls in the audio range. The heavy current drawn by the RF transmitter causes any conductors supplying current to the transmitter to radiate this inductive EMI. Additionally, many other components of the phone, such as the backlight for the display, the display itself, and the keypad, utilize strobing techniques that generate EMI.
One potential solution to overcoming the EMI is to boost the desired inductive signal of the HAC device to a level that overpowers the EMI. If the inductive field of the device is strong, the telecoil can be used with relatively low amplification of the received signal and, thus, relatively low amplification of any EMI. However, if the inductive field is comparatively weak, the amplification of the signal, and, thus, any EMI, needs to be increased to obtain an adequate signal. Further complicating the problem, varying amounts of EMI may be present in the environment, such that the inductive signal level required to overcome the EMI cannot be predetermined.
Still further, the generation of the boosted inductive signal creates a power drain on HAC device that is proportional to the level of the boosted signal. This power drain will shorten the operating time of HAC devices having a “power budget”, such as battery powered wireless telephones. Thus, generating a larger signal will significantly reduce the length of time that the HAC device can operate, whereas a weaker signal may be adequate to overcome the EMI.
Thus, there is a need for a system and method for optimizing the strength of the inductive field of a hearing aid compatible device that is strong enough to overpower ambient EMI, yet having minimal power drain on the device's battery.
Additionally, certain classes of hearing aids have an issue with reorientation, or shifting, of the telecoil during the manufacturing process. More specifically, ITC (In The Canal) and CIC (Completely In the Canal) hearing aid classes are manufactured using techniques allowing most or all of the hearing aid electronics to be molded into a unit that fits into the ear canal. However, in doing so the telecoil can wind up in virtually any position. Optimal coupling of the inductive signal into the telecoil occurs when the signal field is parallel to the telecoil. Thus, the user may have to twist the HAC device around until a “sweet spot” is found, often resulting in a position of the device that is not optimal for its operation.
Thus, there is also need for a system and method for optimizing the orientation of the inductive field of a hearing aid compatible device for coupling the inductive signal into the telecoil.